Vigorous exercise is known to cause transient bronchoconstriction in school children with asthma, many of whom initially have normal lung function at rest. The presence and extent of this phenomena in early childhood is difficult to recognize, because exercise induced bronchoconstriction (EIB) may not limit the child's performance and the child may fail to notice the symptoms until taking part in organized or competitive sport. Conversely, as children do participate in vigorous activities all day long, severe EIB may provoke a crucial disabling condition in the child.